JPH06326384A - Semiconductor laser element drive circuit - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser element drive circuit, which controls constant light output without using a laser beam for monitor. CONSTITUTION:An impedance variable element TR1 connected in series to a semiconductor laser element LD is provided, a voltage in a resistor R, to respond to a drive current of the element LD and a voltage, which is generated responding to this environmental temperature obtainable by detecting the environmental temperature of the element LD by a thermistor Th1, are compared with each other by a comparison amplifier OP1, and the element TR1 is controlled responding to an output voltage, which is outputted responding to the compared result, to set the light output of the element LD so as to become constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device driving circuit for adjusting the optical output of a semiconductor laser device to a constant level.

[0002]

2. Description of the Related Art In a semiconductor laser device, the optical output fluctuates as the device temperature fluctuates. Therefore, conventionally, in order to obtain a constant light output even if the element temperature changes, the laser light for monitoring output from the rear end surface of the semiconductor laser element is detected by a photodiode, and the intensity of this laser light for monitoring is detected. APC (Auto
matic power control) function is provided.

FIG. 5 is a circuit diagram showing a conventional drive circuit with an APC function.

DC power supply voltage + V _cc is a semiconductor laser device L
It is applied to the anode of D, its cathode is connected to the collector of a transistor TR which is an impedance variable element, and its emitter is grounded via a resistor R ₅₁ .

The DC power supply voltage + V _cc is applied to the cathode of the PIN photodiode PD arranged on the rear end face side of the semiconductor laser element LD, and the anode thereof is grounded via the resistor R ₅₂ . The anode of the PIN photodiode PD is connected to the minus (-) input terminal of the comparison amplifier OP, and the output terminal thereof is connected to the base of the transistor TR via the resistor _R53 . A grounded capacitor C is connected between the resistor R ₅₃ and the transistor TR. The positive (+) input terminal of the comparison amplifier OP has a negative power supply terminal grounded to a reference power supply V _r (reference voltage:
_Vr ) is connected to the positive power supply terminal.

In such a circuit, the semiconductor laser device LD is driven by applying the DC power supply voltage + V _cc ,
The laser light is output from the front end face and the monitor laser light is output from the rear end face.

This monitor laser light is a PIN photo diode.
Light is received by the iodine PD, and the photo sensor
An electromotive current I is generated in the ion PD. This electromotive current I is
Anti-R ₅₂Flowing through the voltage V_M(= I ・
R₅₂) Occurs. The comparison amplifier OP has this voltage V
_MAnd the reference voltage V_rAnd the voltage V_MIs constant
Voltage is applied to the base of the transistor TR
To control the light output of the semiconductor laser device LD to a constant value.
It

[0008]

[Problems to be Solved by the Invention] However, the above A
The drive circuit with the PC function is used for a semiconductor laser device that does not output the monitoring laser light, such as a semiconductor laser device that emits a small laser light for monitoring (for example, the reflectance on the rear end face side is high) or a surface emitting semiconductor laser device. When the light reflected by the external optical system or the like is incident on the photodiode PD, it is difficult to accurately receive the monitor laser light, and it is difficult to adjust the light output to a constant level.

Therefore, it is an object of the present invention to provide a semiconductor laser device driving circuit for adjusting the light output to a constant level without using a monitor laser beam.

[0010]

A semiconductor laser device driving circuit according to the present invention responds to a semiconductor laser device, an impedance variable device connected in series with the semiconductor laser device, and a drive current for driving the semiconductor laser device. The current-voltage converting means for generating the first voltage, the temperature-voltage converting means for generating the second voltage according to the environmental temperature of the semiconductor laser device, and the first voltage and the second voltage are compared. The impedance variable element is controlled so that the optical output of the semiconductor laser element becomes constant according to the output voltage output from the comparison amplifier.

[0011]

According to the structure of the present invention, the first voltage according to the drive current obtained by the current-voltage converting means and the second voltage according to the ambient temperature of the semiconductor laser device obtained by the temperature-voltage converting means.
Is controlled by a comparator amplifier to control the impedance variable element connected in series with the semiconductor laser element so that the optical output of the semiconductor laser element becomes constant according to the output voltage obtained by the comparison amplifier. No need to use light.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor laser device driving circuit according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a semiconductor laser device driving circuit of this embodiment.

Semiconductor laser device (laser diode)
A voltage + _Vcc is applied to the anode of the LD, its cathode is connected to the collector of a transistor TR _{1 which} is an impedance variable element, and its emitter is grounded via a resistor R ₁ which is a current-voltage converting means. The output terminal of an operational amplifier OP ₁ which is a comparison amplifier is connected to the base of the transistor TR ₁ via a resistor R ₂ .

The operational amplifier OP₁Plus (+) input
Temperature-voltage conversion means is connected to the terminal. That is,
The input terminal of the resistor R₃And resistance R_FourThrough the negative electrode side
Grounded reference power source V_r1(Reference voltage: V_r1) And the positive electrode side
Connected and fixed voltage + V_h1(V_h1> V_r1) Is a mark
Environmental temperature (ambient temperature) detection with added negative temperature coefficient
Demand thermistor T_h1(Hereafter, this resistance value is R_h1Will be written)
Is the resistance R₃Connected through. Negative temperature
Thermistor T with coefficient_h1Is the temperature
If R is high, the resistance R_h1Is smaller and the temperature is lower
In case of resistance R _h1Grows larger. Also this thermistor
T_h1Is related to the element temperature of the semiconductor laser element LD
It should be provided by properly insulating the part where the ambient temperature can be detected.
For example, a heat sink for mounting the semiconductor laser device LD
It may be provided on the ground, and the semiconductor laser element LD is hermetically
In this cap, if it is installed in
May be appropriately provided in the semiconductor laser device L if possible.
You may make it adhere to D.

The negative (-) input terminal of the operational amplifier OP ₁ is grounded via the resistor R ₅ and the resistor R ₁ .

The semiconductor laser device LD has a constant light output.
Operating temperature I with increasing element temperature _OPIncreases almost monotonically
Therefore, in this circuit, a constant light output is obtained at the element temperature.
Operating current I_OPIs V_B(Voltage V_BIs for the element temperature increase
Increase almost monotonically) / R₁Is set to be
It Incidentally, the transistor TR of this embodiment₁Is the current gain
Since it is large, the driving current I of the semiconductor laser element LD is large._OPAnd
Anti-R₁Current I flowing through₁Are almost equal.

In such a circuit, in the operating state including the initial state, a current I ₁ flows through the resistor R ₁ and the _first terminal of V _A = I ₁ · R ₁ is applied to the negative terminal of the operational amplifier OP 1. A voltage is applied. Further, a current I ₂ = (V _h1 −V _r1 ) / (R _h1 + R ₄ ) flows through the thermistor T _h1 and the resistor R ₄ ,
The positive terminal of the operational amplifier OP ₁ has a reference voltage V _r1
And resistance R _h1 and resistance R _{4 of} the thermistor T _h1 depending on temperature
The second voltage V that is the sum of the voltage divided by
_B = V _r1 + I ₂ · R ₄ is applied.

The operational amplifier OP ₁ compares the voltage V _A with the voltage V _B and applies a voltage corresponding to the result to the base of the transistor TR ₁ to generate the current I ₁ , that is, the semiconductor laser element LD. Drive current I _OP is controlled so that the optical output becomes constant. More specifically, a semiconductor laser device LD
Element temperature rises and voltage V _B increases (V _B > V
_{In the} case of _A ), the current applied to the base is increased, and as a result, the applied current I _OP of the semiconductor laser device LD is increased, and finally the voltage V _A is increased to the voltage V _B. The drive current I _OP is adjusted to be equal. On the contrary, when the temperature of the semiconductor laser device LD is lowered and the voltage V _B is decreased (V _B <V _A ), the current applied to the base is decreased, and as a result, the semiconductor laser is reduced. The drive current I _OP of the element LD decreases and finally the voltage V
I applied current I to be equal to the voltage V _{B that A} is reduced
_OP is adjusted.

In this circuit, the magnitude of the optical output of the semiconductor laser element LD can be set by the set value of the resistor R ₁ . Further, the resistors R ₂ , R ₃ and R ₅ can be omitted.

In this circuit, the semiconductor laser device LD
Has an optical output of 100 mW (operating current I _OP at a temperature of 25 ° C is 2
When operating at a constant current of 80 mA, the operating current I _OP is α = 0.62 mA / ° C with respect to the temperature increase at the thermistor T _h1 position
The thermistor T _h1 (having a resistance R _h1 of 1 KΩ at a temperature of 25 ° C.) in which a resistance R _{4 of} 384 Ω is connected in series has a characteristic of monotonically increasing at 1 V between them. When the generated voltage has a characteristic of increasing substantially monotonically at β = 5.67 mV / ° C with respect to an increase in temperature, the resistance R ₁ is set to about 9Ω from the following equation (1).

Α · R ₁ = β (1) Further, the voltage V _r1 is set to about 1.9 V from the following equation (2).

I _{OPR 1} = V _r1 + _{1R 4} / (R ₄ + R _h1 ) ... (2) The value of the resistor R ₄ depends on the voltage change of the thermistor T _h1 with respect to temperature change. Is set by a conventionally known calculation method so as to be linear.

In such a circuit, it is not necessary to use the laser light for monitoring, and the environmental temperature of the semiconductor laser device PD is detected as the voltage V _B depending on the resistance R _h1 of the thermistor T _h1 , and this voltage V _B is detected. The operational amplifier OP ₁ compares the voltage V _A corresponding to the current I ₁ with the resulting voltage, and the base voltage of the transistor TR ₁ is changed by the resulting voltage to change the drive current I _OP and the semiconductor laser device L.
The light output of D can be adjusted to be constant.

Next, a second embodiment will be described with reference to the circuit diagram shown in FIG.

A voltage + V _cc is applied to the anode of the semiconductor laser element LD, the cathode thereof is connected to the collector of the first transistor TR _{11 which} is an impedance variable element, and the emitter thereof is a resistor R _{11 which} is a current-voltage converting means. Grounded through. This transistor TR ₁₁
The base of is the second transistor TR, which is a comparison amplifier.
_Twelve collectors are connected and their bases are grounded via the resistor R ₁₁ .

The second transistor TR₁₂The emitter of
Has a resistance R₁₂And a thermistor T having a negative temperature coefficient
_h11(The resistance is R_h11, Are connected in parallel,
Resistance R ₁₂And the thermistor T_h11Power supply V across₁₁(Den
Pressure: V₁₁) Is connected.

The negative electrode of the power source V ₁₁ is the reference power source V _11.
It is connected to the positive electrode of _r12 (reference voltage: V _r12 ) and its negative electrode is grounded. With this configuration, the temperature-voltage conversion means is configured.

The thermistor T _h11 may be provided by appropriately insulating it at a portion where the ambient temperature related to the element temperature of the semiconductor laser element LD can be detected. For example, it is provided on a heat sink or the like on which the semiconductor laser element LD is mounted. Also, when the semiconductor laser element LD is installed in a closed cap, it may be appropriately provided in this cap, and if possible, it may be brought into close contact with the semiconductor laser element LD.

The semiconductor laser device LD has a constant light output.
Operating temperature I with increasing element temperature _OPIncreases almost monotonically
Therefore, in this circuit, a constant light output is obtained at the element temperature.
Operating current I_OPIs {V_B(Voltage V_BIs against the increase in element temperature
And then increases almost monotonically) -V_BE(Second transistor T
R₁₂Voltage between base and emitter of: constant)} / R₁₁so
Is set to be. In addition, this first tran
Dista TR₁₁Has a large current amplification factor, so a semiconductor laser
Drive current I of element LD_OPAnd resistance R₁₁Current I flowing through ₁₁Is
Almost equal.

[0030] In斯Ru circuit comprises the resistor R ₁₁ current I ₁₁
Flows to the base of the transistor TR ₁₂ and V _A1 =
A first voltage of I ₁₁ · R ₁₁ is applied.

Further, the transistor TR₁₂The emitter of
Is a thermistor T that is temperature dependent _h11Resistance R_h11And
Anti-R₁₂Voltage V₁₁Is divided by the voltage V_r12
The second voltage V shown in equation (3)_B1Is applied
It

V _B1 = V ₁₁ · R ₁₂ / (R ₁₂ + R _h11 ) + V _r12 (3) The second transistor TR ₁₂ compares the voltage V _A1 with the voltage V _B1 and A voltage corresponding to the result is applied to the base of the first transistor TR ₁₁ , and the current I ₁₁ , that is, the drive current I _OP (I _OP is substantially equal to I ₁₁ ) is controlled so that the light output becomes constant. .

That is, when the temperature of the semiconductor laser device LD rises and the voltage V _B1 increases (V _B1 > V _A1 + V _BE ), the voltage applied to the emitter of the second transistor TR ₁₂ is increased. Becoming larger, the first transistor TR ₁₁
The current applied to the base of is increased. As a result, the current I ₁₁
Is increased, and finally the current I ₁₁ is adjusted so that the voltage (V _A1 + V _BE ) becomes equal to the increased voltage V _B1 . On the contrary, when the temperature of the semiconductor laser device LD drops and the voltage V _B1 becomes small (V _B1 <V _A1 + V _BE ),
The current applied to the base of the first transistor TR ₁₁ is reduced, and as a result, the current I ₁₁ is reduced so that the voltage (V _A1 + V _BE ) is finally equal to the reduced voltage V _B1. The current I ₁₁ is adjusted.

In this circuit, the magnitude of the light output of the semiconductor laser element LD can be set by the set value of the resistor R ₁₁ . The set value of each element is set by the same method as in the first embodiment.

Next, a third embodiment will be described with reference to the circuit diagram shown in FIG. The difference from the second embodiment is that the power supply V ₁₁ and the power supply V _r12 used in the second embodiment are replaced by variable resistors and a constant current diode is used. Are denoted by the same reference numerals and the description thereof is omitted.

The voltage + V _cc is applied to the anode of the semiconductor laser device LD and also to the temperature-voltage conversion means. That is, the constant current diode D ₁ is applied to the anode and its cathode is grounded through the thermistor T _h11 and the variable resistor VR ₁ and the variable resistor VR ₂ connected in parallel to the resistor R ₁₂ in this order. The resistances R _h11 and R ₁₂ of the thermistor T _h11 are set so that VR ₁ << R _h11 + R ₁₂ .

Since such a circuit passes through the constant current diode D ₁ , a constant current I ₂₁ flows through the variable resistor VR ₂ . The resistance values of the variable resistor VR ₁ are the resistances R _h and R ₁₂
Current I ₂₁ substantially flows through the variable resistor VR ₁ as well. As a result, the variable resistors VR ₁ and VR ₂ respectively function as a constant voltage power source having a voltage of I ₂₁ · VR ₁ and a constant voltage power source having a voltage of I ₂₁ · VR ₂ . In other words, the variable resistors VR ₁ and VR ₂ have the same functions as the first power source V ₁₁ and the power source V _{r12 of} the second embodiment, respectively.

Therefore, since the same function as that of the second embodiment is performed, the same effect as that of the second embodiment can be obtained. Further, by changing the resistance values of the variable resistors VR ₁ and VR ₂ , it is possible to easily deal with the semiconductor laser elements LD having different characteristics. When used exclusively for a specific semiconductor laser device, the variable resistors VR ₁ and VR ₂ may be replaced by simple resistors or constant voltage diodes.

Next, a semiconductor laser device driving circuit according to the fourth embodiment will be described with reference to the circuit diagram shown in FIG. This circuit is a circuit exclusively used for a semiconductor laser device having a specific property as in the second embodiment, and is further simplified as compared with the second and third embodiments. The same parts as those in the second embodiment are designated by the same reference numerals and the description thereof will be omitted.

The voltage + V _cc is applied to the anode of the semiconductor laser device LD and also to the temperature-voltage conversion means. That is, it is connected via a resistor R ₁₃ to the cathode of a constant voltage diode D ₂ connected in parallel to the thermistor T _h11 and resistor R ₁₂ , and its anode is grounded.

In such a circuit, a constant voltage is applied to the thermistor T _h11 and the resistor R ₁₂ by the constant voltage diode D ₂ , and this voltage is _divided by the resistors R _h11 and R _{12 to} generate the second transistor TR. Applied to ₁₂ emitters.

In such a circuit, the power source V _r12 in the second embodiment is used.
Although the portion corresponding to is omitted, by selecting the resistance value of the resistor R ₁₁ , the constant voltage diode D ₂ can be changed to the second
Since it functions in the same manner as the power source V ₁₁ of the embodiment, the same effect as that of the second embodiment can be obtained.

When the thermistors T _h1 and T _h11 are thermistors having a positive temperature coefficient, T _h1 and R ₄ are used.
The position of T _h11 and the position of R ₁₂ may be exchanged.

[0044]

The semiconductor laser device driving circuit of the present invention is
A variable impedance element connected in series to the semiconductor laser element, a current-voltage converting means for generating a first voltage according to a drive current for driving the semiconductor laser element, and a first variable voltage element depending on an environmental temperature of the semiconductor laser element. A temperature-voltage converting means for generating a voltage of 2; and a comparison amplifier for comparing the first voltage and the second voltage, wherein the impedance variable element is provided in accordance with the output voltage output from the comparison amplifier. Since the light output of the laser element is controlled to be constant, the present invention does not need to use the monitor laser light.

As a result, it can be used for a semiconductor laser device that does not output a monitoring laser beam, such as a semiconductor laser device that emits a small monitoring laser beam or a surface-emitting type semiconductor laser device. It is also suitable in the case of a configuration that cannot be performed.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a semiconductor laser device driving circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a semiconductor laser device driving circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a semiconductor laser device driving circuit according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a semiconductor laser device driving circuit according to a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram showing a conventional semiconductor laser device driving circuit.

[Explanation of symbols]

LD semiconductor laser element TR ₁ transistor (impedance element) OP ₁ operational amplifier (comparison amplifier) R ₁ , R ₁₁ resistance (current-voltage conversion means) R ₄ , R ₁₂ resistance (temperature-voltage conversion means) T _h1 , T _h11 thermistor (temperature Voltage conversion means) TR ₁₁ first transistor (impedance element) TR ₁₂ second transistor (comparison amplifier)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toyzo Nishida 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (1)

[Claims] 1. A semiconductor laser device, an impedance variable device connected in series to the semiconductor laser device, and a current-voltage conversion means for generating a first voltage according to a drive current for driving the semiconductor laser device, A temperature-voltage conversion unit that generates a second voltage according to the ambient temperature of the semiconductor laser device and a comparison amplifier that compares the first voltage and the second voltage are provided, and the output output from the comparison amplifier A semiconductor laser device driving circuit, wherein the impedance variable device is controlled so that the optical output of the semiconductor laser device becomes constant according to a voltage.